[vsnet-grb-info 5307] GRB 071025: Swift-XRT Team refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6998
SUBJECT: GRB 071025: Swift-XRT Team refined analysis
DATE:    07/10/25 14:14:05 GMT
FROM:    Claudio Pagani at PSU/Swift-XRT  <pagani at astro.psu.edu>

C. Pagani, D. N. Burrows, J. Racusin (PSU), P. Evans (U Leicester) report on
behalf of the Swift-XRT Team:

We have analysed the first three orbits of Swift-XRT data obtained for GRB
071025 (Pagani et al. GCN Circ. 6986), totalling 250 s of Windowed Timing (WT)
data and 2.7 ks of Photon Counting (PC) data.

Using 1189 seconds of overlapping XRT Photon Counting mode and UVOT V-band data,
we find an astrometrically corrected X-ray position (using the XRT-UVOT
alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec =
355.07142, 31.77857 which is equivalent to:

RA (J2000):  23 40 17.14
Dec (J2000): +31 46 42.9

with an uncertainty of 1.7 arcsec (radius, 90% confidence). This is 7.1 arcsec
from the refined XRT position (GCN Circ. 6990) and 0.7 arcsec from the optical
afterglow found by ROTSE-III at McDonald Observatory (Rykoff et al., GCN Circ.
6987).

The bright X-ray light-curve can be fitted by a broken power-law, with an
initial steep decay index of 2.8 +/- 0.3  followed by a flatter decay index of
1.5 +/- 0.1 after a break at 260 +/- 20 seconds.

The WT data (150-400 seconds) can be modelled as an absorbed power-law, with
Gamma = 1.40 +/- 0.05 and a total absorbing column of NH = (0.9 +/- 0.1)e21
cm^-2, in excess of the Galactic value of 5.1e20 cm^-2. The 0.3-10 keV observed
(unabsorbed) flux during this time is 2.0e-09(2.2e-09) erg cm^-2 s^-1.

Assuming the source continues to decay with the same decay index of 1.5, we
predict an XRT count rate of 7E-3 counts/s at T+24 hours, which corresponds to
an observed flux of 4E-13 ergs cm^-2 s^-1.

This circular is an official product of the Swift-XRT team.